Impulse recording optical system



Feb. 6, 1951 J.'A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM 5 Sheeis-Sheet 1 Original Filed Aug. 2, 1940 I Lfl ENTOR JOHN .MAURERJR.

AGENT 5 Sheets-Sheet 2 FIGG FIGS

J. A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM FIGQS FIGS Feb. 6', 1951 Original Filed Aug. 2, 1940 FIG4 FIG]

Feb. 6, 1951 J. A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM 5 Sheets-Sheet 3 Original Filed Aug. 2, 1940 PIC-HI FIGJB FIGJZ FIG. 20

FIGIS INVENTOR JOHN A. MAURER, a By WW AGENT Feb. 6, 1951 J. A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM 5 Sheets-Sheet 4 Original Filed Aug. 2, 1940 FIG. I3

FIG. l4

FIG. l5

IN V EN T 0R Jaw AMAURERMR.

AGE/VT Feb. 6, 1951 J. A. MAURER, JR

IMPULSE RECORDING OPTICAL svsma 5 Sheets-Sheet 5 Original ,Filed Aug. 2, 1940 FIGIE: PRIOR AR'R'HORIZONTAL PLANE.

FIG. I7A: PRIOR A E7RT|CAL PLANE I l F'IG.I7B: PRIOR ART, HORIZONTAL PLANE INVENT OR JR. WW

- AGENT v JDHN AMA (/kER,

'-- was Feb. 6,1951

IMPULSE RECORDING OPTICAL SYSTEM John A. Maurer, In, New York, N. Y., assignor to J. A. Maui-er, Inc., New York, N. Y., a corporation of New York briginalapplication August 2, 1940, Serial No.

Divided and this application November 21, 1944, Serial No. 564,452

9 Claims. 1

This invention relates to optical systems for the photographic recording of electrical impulses on a moving film such as are used in sound recording, picture transmission, and the like, and this application is a division'of my application Serial No. 349,515, filed August 2, 1940, now abandoned,

which was also assigned to J.'A. Maurer, Inc.

More particularly, the invention relates to optical systems of the class referred to above wherein a small mirror vibrated by an oscillograph galvanometer, .or a similar device for translating electrical impulses into mechanical vibrations, modulates a light beam in accordance with the electrical impulses to be recorded. To that end, an opening in a screen is illuminated by light flux from the recording light source, such as the filament of an incandescent lamp, and an image of the illuminated opening is formed in mirror.

the plane of a horizontal slit where it, in its turn,

illuminates a portion of the slit. The image of the opening is moved by the vibration of the oscillograph mirror either vertically across the slit or in a horizontal direction lengthwise of the slit. In this manner, the illuminated portion of the slit is varied in length or in illumination. The slit, furthermore, is imaged at the recording point by a lens, or lens system, with respect to which the recording point is conjugate to the slit in the two co-ordinate planes of the optical system. The recording point is the point at which the optical axis of the system strikes the film, and the film moves past the recording point in a substantially vertical direction.

The mirror oscillograph recording optical systems known heretofore, however, have the disadvantage that the light flux from the recording light source is not efliciently utilized therein. Since the imagery of the illuminated opening in the plane of the slit is performed in those optical systems so that the light flux emanating from the opening is diffused at the oscillograph mirror in the two co-ordinate planes, the aperture of the mirror is the limiting aperture in both coordinate planes. But the mirror aperture cannot be enlarged beyond a certain degree because the physical size of the mirror mustbe comparatively small in order to avoid distortions due to. its mass. For a given recording light source, therefore, the amount of light flux reaching the slit is unduly limited in the prior art optical systems, and this limitation makes itself particularly felt when filters are used at some position in the optical system, for example, for selecting light rays of a certain wave length, or for other pur- P086.

- 2 Another drawbackof theknown mirror oscillograph recording optical systems is that a portion of the light flux from the recording light source is not eifectively prevented therein from falling on parts other than the oscillograph mirror, or on the structure housing the optical system. This portion of the light flux is to some extent reflected diffusely, thus forming stray light even though the surfaces on which it is incident may be black. Such stray light is objectionable because it may cause an additional exposure of the moving film, which should be exposed only to light flux modulated by the oscillograph It is, therefore, the primary object of the present invention to provide a mirror oscillograph recording optical system which is highly eflicient as regards the utilization of the light flux from the recording light source.

Another object of the invention is the provision of such an optical system whose limiting aperture can, in one of its co-ordinate planes, be made much larger than the aperture of the oscillograph mirror.

Another object of the invention is the provision of such an optical system wherein the formation of stray light is reduced to a negligible amount.

Another object of the invention is the provision of such an optical system which is particularly satisfactory as regards ease of manufacture an convenience of adjustment.

Another object of the invention is the provision of such an optical system which may be designed very compactly.

Still other objects of the invention include thosewhich are hereinafter stated or apparent, or which are incidental to the invention.

In order to attain its objects, the invention proposes the formation of an image of the illuminated opening in the plane of the slit by means of an imagery which isdifferent in the two coordinate planes of the optical systems. In the co-ordinate plane at right angles to the axis of vibration of the oscillograph mirror, the opening is imaged immediately at the slit by the action of imaging means acting in that plane in which, therefore, the light flux from the opening is diffused at the mirror. This is necessary in order that the image of the opening may be movable by the vibration of the mirror. But in the coordinate plane which contains the axis of vibration of the mirror, an intermediate image of the ope is formed substantially on the mirror, and t intermediate image is imaged at the slit. The intermediate image is formed by first imaging means and imaged by second imaging means both of which act in only the last mentioned plane. One of the conjugate foci of the second imaging means, therefore, coincides with one of the conjugate foci of the first imaging means. Thus, the mirror is substantially at a common focus of two imaging means which act in only the co-ordinate plane containing its axis. In this plane, therefore, the amount of light flux arriving at the slit from the opening is limited not by the aperture of the mirror, but rather by the aperture of the second imaging means, and

the latter aperture can be made considerably larger than the aperture which it is practical to give to the mirror.-

The opening, in its turn, is illuminated by light flux from the recording light source an image of which is formed substantially on the oscillograph mirror by the action of a condenser lens in the plane at right angles to the mirror axis. Thus,

there is formed substantially on the mirror an image of the recording light source and, simultaneously, the intermediate image of the opening illuminated by that light source. Substantially all the light flux entering the optical system through the opening hence is controlled by the mirror whereby the formation :of stray light is reduced to a negligible amount.

In the foregoing brief explanation of the state of the art and summary of the invention, and throughout the present specification, the term co-ordinate planes" designates two planes at right angles to each other whose line of intersection is the optical axis of the systems. As already stated hereinabove, the oneof the co-ordinate planes contains the axis of vibration of the oscillograph mirror so that the other co-ordinate plane is at right angles also to the mirror axis. As likewise stated hereinabove, the slit employed in the optical systems extends horizontally, while the film moves past the recording point in a sub-- stantially vertical direction. The co-ordinate plane which contains the slit and is at right angles to the direction of the film movement at the recording point, hence is the horizontal plane,

. while the co-ordinate plane at-right angles to the horizontal plane is the vertical plane. Either the vertical or the horizontal plane may contain the mirror axis, as will be shown hereinbelow. The plane of the slit, finally, is the plane which contains the slit, and is at right angles to both the vertical and horizontal planes.

In the present specification, the terms vertical" and horizontal thus are not used in any absolute sense but merely in order to distinguish between two directions, or planes, at right angles to one another, and choice between those terms has been determined solely by convenience in description and illustration.

The invention will be better understood when the following description is considered with the accompanying drawings of certain presently preferred embodiments thereof, and its scope will be pointed out in the appended claims.

In the drawings: 4

Fig. l is a diagrammatic perspective view of an optical system wherein the invention has been embodied,

Fig. 2 is a diagrammatic longitudinal section in the vertical plane of the optical system shown in Fig. 1, the optical axis being represented as a straight line and an oscillograph mirror as an aperture,

Fig. 3 is a corresponding section in the horizontal plane,

Figs. 1 to 3,

' Fig. 12 is a perspective view of a modification of a part shown in Fig. 11,

Fig. 13 is a diagrammatic perspective view of another optical system wherein the invention has been embodied,

Fig. 14 is a diagrammatic longitudinal section in the vertical plane of the optical system shown in Fig. 13, the optical axis being represented as a straight lineand an oscillograph mirror as an aperture,

Fig. 15 is a corresponding section in th horizontal plane,

Fig. 16 is a corresponding section in the horizontal plane of a prior art optical system,-

' Figs. 17A and 17B are corresponding sections in the vertical and horizontal planes, respectively, of another prior art optical system,

Fig. 18 is a perspective view of a modification of another part of the optical system shown in Figs. 1 to 3,- r

Figs. 19 and 20 are perspective views of modifications of a part common to the optical systems of Figs. 1 to 3 and Figs. 13 to 15, and

Fig. 21 is a diagrammatic longitudinal section,

in the vertical plane of another modification of the optical system of Figs. 1 to 3.

Referring first to Figs. 1 to 3, the invention is shown therein as embodied, by way of example, in a variable area recording optical system. The optical system has a light source such as the filament I0 of an incandescent lamp II. The light flux from lamp filament I0 uniformly illuminates a triangular opening l3 in a screen ll so that a uniformly illuminated triangular light spot is formed at screen ll. The light beam defined by lamp filament l0 and opening l3 proceeds through the optical system and is deflected by the mirror I! of an oscillograph galvanometer (not shown) or similar device for translating electrical impulses into mechanical vibrations. It thus has a part which is incident from opening I3 upon mirror l1, and a part which is reflected from mirror I! towards the recording point 27. Recording point 21 is the point at which the optical axis of the system strikes the film 23, and film 23 moves past recording point 21 in a substantially vertical direction as indicated by the arrow=129.

More particularly, opening I3 is 'ani'sosceles triangle whose base extends horizontally, and mirror I! is adapted to vibrate about an axis l8'l 8 which likewise extends horizontally. Furthermore, a horizontal slit 2| is formed in a.

dent part of the light beam proceeding through the optical system. A second cylindrical lens 24 which also has its cylinder axis vertical, is placed between mirror I! and screen 22, while between screen 22 and recording point 21 there is placed a spherical lens System26 which ma be of the type usually employed as a microscope objective.

These five imaging means have focal lengths relative to the other parts of the optical system as follows (see Figs. 2 and 3) Spherical lens |2 has one of its conjugate tool at lamp filament Ill, and the other substantially at mirror II, that is, either on mirror I! or at a position close thereto. Cylindrical lens II has one of its conjugate foci at opening l3, and the other substantially at mirror l1 so that an intermediate image of opening i3 is formed substantially on mirror Spherical lens l9 has one of its conjugate tool at opening I3, and the other 1 at slit 2|. Cylindrical lens 24 has one of its .con-

jugate foci at the intermediate image of opening l3, and the other at slit 2|. Microscope objective 26, finally, has one of its conjugate foci at slit 2 I, and the other at recording point 21.

It will thus be seen that, since microscope objective 26 1s a spherical lens system, recording point 21 is conjugate to slit 2| in the two coordinate planes of the optical system of Figs. 1 to 3 and, furthermore, that slit 2| is illuminated in this optical system by means of the followin imagery:

In the vertical plane (Fig. 2), spherical lens I! forms an image of the uniformly illuminated opening |3 in the plane of the horizontal-slit 2| Likewise in the vertical plane, spherical lens l2 forms an image of lamp filament l substantially on mirror l1, thereby filling mirror I! with light and also aiding in the uniform illumination ,of opening lit by lamp filament III.

In the horizontal plane (Fig. 3) cylindrical lens l forms substantially on mirror l1 the intermediate image of opening l3, and an image of the intermediate image is formed by cylindrical lens 24 in the plane of slit 2 I. Cylindrical lenses 5 and 24 do not interfere with the imagery in the vertical plane since they have their cylinder axes vertical, and hence act in only the horizontal plane. Spherical lenses l2 and IS, in their turn, have power alsoin the horizontal plane. But their actions in this plane can be disregarded for the following reasons:

On account of its position and relative focal length, spherical lens l2 tends to image lamp filament |0 substantially on mirror also in the horizontal plane. The action, however, of cylindrical lens l5 interferes with this imager to such an extent that it becomes immaterial for attaining the objects of the present invention. On the other hand, the power of spherical lens IS in the horizontal plane has no effect upon the actions of cylindrical lenses l5 and 24 on account of the proximity ofspherical lens l9 to mirror which is, in the horizontal plane, substantially at a common focus of cylindrical lenses l5 and 24. No actions, therefore, of spherical lenses l2 and I9 have been indicated in Fig. 3.

Thus, an image of opening I3 is formed in the plane of slit 2| by the action of spherical lens IS in the vertical plane, and the actions of cylindrical lenses l5 and 24 in the horizontal plane. Slit 2|, therefore, is conjugate to opening l3 in both the vertical and horizontal planes so that image 25 is a uniformly illuminated triangular light spot which illuminates a portion of slit 2|. Furthermore, the light flux from opening 1 3 is brought to a focus substantially on mirror in only the horizontal plane (see Fig. 3), while it is diifused at mirror H in the vertical plane (see Fig. 2), that is, the plane through which the light beam is deflected when mirror |1 vibrates about the horizontal axis |8|8. Image 25 hence is moved vertically across slit 2| by the vibra- 6 tion of mirror l1, whereby the illuminated poitionoi slit 2| is varied in length. [If the light flux from opening l3 were brought to a focus at mirror II in the vertical plane, or in both the vertical and horizontal planes, image 25 would not move at all, as will readily be understood by those skilled in the art.]

As seen from microscop objective 28, therefore, the illuminated portion of slit 2| is a horizontal line of light whose illumination is uniform, but whose length varies at both its ends in accordance with the vibration of mirror II. By the action of microscope objective 28 in both the verticaland horizontal planes. this line of light is reproduced at recording point 21. It there exposes film 23 so that the symmetrical variable area track 23 is produced thereon.

The adjustment, finally. of mirror l1 about its horizontal axis |3l3 is as follows;

In the vertical plane, horizontal slit 2| is, with respect to spherical lens l3, conjugate to a horizontal line through opening I3. The particular horizontal line to which slit 2| is conjugate, is determined by the angle of inclination of mirror Normally,.therefore, mirror I1 is adjusted so that at its rest position, that is, when no electrical impulses are applied to the oscillograph g-alvanometer on which it is mounted, slit 2| is conjugate to the broken line w-a, shown in Fig. 4, which passes through opening l3 halfway between its tip and its base. when then the electrical impulses to be recorded are applied in known manner to the oscillograph galvanometer, mirror I! vibrates in accordance therewith so that, when the amplitude of its vibration is a maximum, slit 2| is conjugate to .the broken line bb at the one extreme of its motion, and to the broken line 0-0 at the other extreme thereof; see Fig. 4.

Opening I3 in screen I4 is shown in Figs. 1 and 4. and has been described hereinabove, as being an isosceles triangle whose base. extends horizontally. However, any other opening whose horizontal extension varies in a vertical direction, may' b substituted for opening Hi to produce a variable area track on film 23. For example, the

opening in screen l4 may be a right-angled tri.- angle with one of the sides adjacent to the right angle extending horizontally as is the opening 33 shown in Fig. 5, or there. may one or more saw,- tooth projections extend into itas they do into the openings 3| and 32 shown in Figs. 6 and '7,

respectively.

As has already been pointed out hereinabove, the illuminated portion of slit 2| is in the case of opening I: a horizontal line of light whose length varies at both its ends, so that the symmetrical variable area track 28 is produced on film 23 in this case. With opening, on the .other hand, the illuminated portion of slit 2| is a horizontalline of light whose length varies at only one of its ends, so that the variable area track on film 23 is of the unilateral type as is the track 60 shown in Fig. 13. With opening 3|, furthermore, two horizontal lines. of light, each varying in length at only one of its ends, appear at screen 22 so that two unilateral variable area tracks are produced on film 23. 'With opening 32, finally, there appear at screen 22 three horizontal lines of light, each varying in length at both its ends, so that threesymmetrical variable area tracks are simultaneously produced on film 23. y Tracks of the type known as push-pull? may also be producedon film '23 by combiningin screen I4 two openings of the kind described openingsv 33a and 33b, a class B push-pull symmetrical variabie area track is produced, and with openings 34a and 34b a class B push-pull unilateral variable area track. Class A push-pull variable area tracks may be produced, for example, by providing in screen H two right-angled triangles adjacent to each other along a common side d-d so that together they form a parallelogram 35, as shown in Fig. 10. In a preferred arrangement for the production of class 'A push-pull variable area tracks, however, a portion Ma of screen I4 separates the two rightangled triangles 35a and 35b, as shown in Fig.

in Figs. to a the horizontal line through the opening, or openings, in screen-l4 which is normally conjugate to slit 2| when mirror I! is at As in Fig. 4, the broken line H indicates also 3 straight edges which are inclined with respect to the horizontal plane of the optical system. Since, furthermore, the variation in length of the horizontal line, or lines, of light at screen 22 is effected only by those inclined edges, the lower portion of screen I4 may be omitted if desired, as indicated in Fig. 5 by the broken line e-e, for example.

When any of the openings, or pairs of openings, shown in Figs. 4 to 10a is in screen l4 and receives light flux from lamp filament 0 through spherical lens l2, there is formed at screen H a uniformly illuminated light spot whose horizontal extension varies in a vertical direction, or a pair of such light spots. The light flux emanating from this light spot, or these light spots, hence is vertically graded.

Light spots of vertically graded light flux, however, may also have a uniform horizontal extension and a vertically varying illumination. Means for forming a light ,spot of this type are well known in the art. They may consist, 'for example, of the means disclosed by G. L. Dimmick in his U. S. specifications 2,095,317 and 2,095,318. These means include an opening 36 which is a rectangle with one of its sides extending vertically, and a penumbra stop 31, as shown in Fig. 11.

But the illumination of rectangular opening 26 may also be varied vertically by associating with opening a vertically graded light shading member 38 such as is disclosed, for example, in my U. S. specification 1,955,386 and shown in Fig. 12 of this specification.

When these or other suitable means for forming a light spot of uniform horizontal extension and vertically varying illumination are substituted for opening I: in the optical system of Figs. 1 to 3as shown by way of example in Fig. 11- the illuminated portion of slit 2|, as seen from microscope objective 26, is a horizontal line of light whose length is constant, but whose illumination varies in accordance with the vibration of mirror l|.. Since this line of light is again reproduced by microscope objective 26 at recording point 21, a variable density track 39 is now produced on film 23 as it moves pastrecording point 21.

Whenever the optical system of Figs. 1 to 3 is employed for producing a variable area track and well defined. The horizontal line, or lines.

of light formed at screen 22 and reproduced at recording point 2'! must, therefore, be sharply defined at its, or their, ends. For that reason, cylindrical lenses I5 and 24, and microscope objective 28, should preferably be well corrected for spherical and chromatic aberration, and for coma. However, if these lenses are not so well corrected, the beneficial results accruing from their employment in accordance with the present invention may'still be had, although to a lesser extent than it they are well corrected. By way of further example, the invention is shown in Figs. 13 to 15 as embodied in another variable area recording optical system. In this optical system, the light flux from lamp filament II uniformly illuminates the rectangular opening 25 in the screen I so that a uniformly illuminated rectangular light spot is formed at screen II. The light beam defined by lamp filament II and opening 35 proceeds through the optical system and is again deflected by the oscillograph mirror I! so as to have a part which is incident from opening 35 upon mirror I l, and a part which is reflected from mirror I! point 21.

More particularly, the edge SI of opening 25 extends vertically so that the uniformly illuminated light spot at screen I! has an, edge which extends vertically, and mirror i1 is now adapted to vibrate about an axis 58-58 which likewise extends vertically. The slit 2|, on the other hand, is again horizontal, and it is again formed in the screen 22 which is placed between mirror I! and recording point 21. I

Spherical condenser lens l2 and spherical lens is are again placed adjacent to screen l4 and in towards recording front of mirror II, respectively, and the microscope objective 26 is again 22 and recording point 21. also have the same relative focal lengths as in the case of the optical system of Figs. 1 to' 3. That is to say, spherical lens l2 has one of its conjugate feel at lamp filament ill and the other substantially at mirror ll, spherical lens- I9 has placed between screen one'of its conjugate tool at opening 35 and the the optical system of Figs. 13 to 15. A cylindrical lens 55 which has its cylinder axis horizontal, is placed between screen H and mirror I I, and a cylindrical lens 55 which likewise has its cylinder axis horizontal, is placed between mirror I! and screen 22, while a spherical lens 59 is placed adjacent to screen 22. Cylindrical lens 55 has one 01' its conjugate foci at opening 35, and the other substantially at mirror |1 so that an intermediate image of opening 36 is formed substantially on mirror I1. Cylindrical lens 55 has one of its conjugate feel at the intermediate image of opening 35, and the other at slit 2|. Spherical lens 59, finally, has one of its conjugate tool at mirror l1, and the other substantially at microscope objective 25; see Figs. 14 and 15.

15 By virtue of the above arrangement, slit 2| is on film 22, it is desirablethat the boundarmor Lenses |2, |9, and 25, j

illuminated in the optical system of Figs. 18 to 15 as follows:

In the vertical plane (Fig. 14) cylindrical lens 55 forms substantially on, mirror II the intermediate image of the uniformly illuminated opening 36, and an image of the intermediate image is formed by cylindrical lens 56 in the plane of the horizontal slit 2|.

In the horizontal plane (Fig. 15) spherical lens l3 forms an image of opening 3-6 in the plane of slit 2 Likewise in the horizontal plane, sperical lens l2 forms an image of lamp filament Ill substantially on mirror l1, and an image of mirror I1 is formed by sperical lens 53 on, or in the neighborhood of, microscope objective 26. The action of spherical lens |2 fills mirror l1 with light and also aids in the uniform illumination of opening 35 bylamp filament Ill. The action of spherical lens 59, on the other hand, concentrates, in the horizontal plane, the light fiux passing through slit 2| for any given angular position of mirror N. This action is necessary because cylindrical lenses 55 and 56 have their cylinder axes horizontal and hence no power in the horizontal plane, which plane contains slit 2|.

Since they act in only the vertical plane,.cylindrical lenses 55 and 56 do not interferewith the imagery in the horizontal plane. Spherical lenses l2 and IS, in their turn, have power also in the vertical plane. But their actions in this plane can be disregarded for the reasons set forth hereinabove with respect to their actions in the horizontal plane of the optical system of Figs. 1 to 3. No actions, therefore, of spherical lenses [2 and I! have been indicated in Fig. 14. The action, finally, of spherical lens 59 in the vertical plane is barred by screen 22. Spherical lens '59 hence may be replaced by a cylindrical lens having the same relative focal length and aperture, and having its cylinder axis vertical so that it acts in only the horizontal plane.

Thus, an image 51 of opening 36 is formed in the plane of slit 2| by the actions of cylindrical lenses 55 and 56 in the vertical plane, and the action of spherical lens IS in the horizontal plane. Slit 2|, therefore, is conjugate to opening 36 in both the vertical and horizontal planes so that image 51 is a uniformly illuminated rectangular light spot which illuminates a portion of slit 2|. Furthermore, the light flux from opening 36 is brought to a focus substantially on mirror I1 in only the vertical plane (see Fig. 14), while it is diffused at mirror H in the horizontal plane (see 'Fig. 15), that is, the plane through which the light beam is deflected when mirror l1 vibrates about the vertical axis 58-58. Image 51 hence is moved in a horizontal direction lengthwise of slit 2| by the vibration of mirror |1, whereby the illuminated portion of slit 2| is varied in length. There thus appears at screen 22 again a horizontal line of light whose illumination is uniform, but whose length varies at one of its ends in accordance with the vibration of mirror |1. This line of light is again reproduced at recording point 21 by the action of microscope objective 26 in both the vertical and horizontal planes. Moreover, film 23 moves past recording point 21 again in a substantially vertical direction as indicated by the arrow 29 so that the unilateral variable area track 60 is now produced on film 23. When, therefore. the electrical impulses to be recorded are applied in known manner to the oscillograph galvanometer on which mirror I1 is mounted. track 60 is a record of those impulses.

act in only the horizontal plane.

The length of the line of light at screen'22 mice at only one of its ends because the optical system is shown in Fig. 13 as being adjusted so that the image of only the vertical edge 6| of opening 36 intersects slit 2|. However, the optical system may also be designed and adjusted so that the images of both vertical edges 6| and 62 of opening 3-6 intersect slit 2|, in which case a class A push-pull variable area track is produced on film 23.

In place of rectangular opening 38, screen ll may, in the optical system of Figs. 13 to 15, have any other opening permitting the formation, in the manner described hereinabove, of an image thereof whose movement lengthwise of slit 2| varies the length of the illuminated portion of silt 2|. All that is required to accomplish that end, is that the opening in screen II have at least one edge whose image transversely intersects slit 2|, and this edge need not be straight, as are edges 6| and 52, but may be curved or even ragged, if desired.

The two optical systems of Figs. 1 to 3 and Figs. 13 to 15 thus are alike in that in both of them recording point 21 is conjugate to horizontal slit 2|, and slit 2| to an illuminated opening in screen H, in the two co-ordinate planes. image of the opening, therefore, is formed in the plane of slit 2|, and this image is obtained by means of an imagery whose novelty resides in the fact that it is different in the two co-ordinate planes. In the co-ordinate plane at right angles to the axis of vibration of mirror H the opening is imaged immediately at slit 2| by the action of imaging means acting in that plane. But in the co-ordinate plane which contains the mirror axis, an intermediate image of the opening is formed substantially on mirror I 1. and this intermediate image is imaged at slit 2 I, the intermediate image being formed by imaging means acting in only the last mentioned plane and being imaged by such means. Since, for example, mirror axis |8|8 is horizontal, opening I3 is, in the optical system of Figs. 1 to 3, imaged immediately at slit 2| by the action of spherical lens IS in the vertical plane, while'an intermediate image of opening I3 is formed substantially on mirror H by cylindrical lens I 5 and imaged at slit 2| by cylindrical lens 24, which two cylindrical lenses Since, on the other hand, mirror axis 5858 is vertical, opening 36 is, in the optical system of Figs. 13 to 15, imaged immediately at slit 2| by the action of spherical lens IS in the horizontal plane, while an intermediate image of opening 36 is formed substantially on mirror H by cylindrical lens 55 and imaged at slit 2| by cylindrical lens 56, which two cylindrical lenses act in only the vertical plane.

As has been set'forth hereinabove, the opening in screen I4 must be imaged immediately at slit 2| in the co-ordinate plane at right angles tothe axis of mirror l1 because the light flux from the opening must, in this plane, be diffused at mirror H in order that the image of'the opening may be movable by the vibration of mirror |1. That it is highly desirable to form, in the co-ordinate plane containing the axis of mirror |1, an inter-- mediate image of the opening substantially on mirror l1 and to image this intermediate image at slit 2|, will now be shown:

stantially on mirror l1 by cylindrical lenses I5 a .ll and 55, respectively, and imaged atslit 21 by cylindrical lenses '24 and G, respectively. The

cylinder axes of lenses I! and 24 are at right angles to mirror axis l8i8,. and the cylinder axes of lenses '55 and 58 are at right angles to mirror axisfiB-SB. Mirror I! thus is substantially at a common focus of two imaging meanswhich act in only the. co-ordinate plane containing its axis. In this plane. therefore, the amount of light flux arriving at slit 2! from the'opening cylindrical lenses 24 and 56, however, can be made as much as five. times larger than the aperture which it'is' practical to give to mirror l1.

On account of the last mentioned feature, the

y novel imagery performed in the optical systems .of Figs. 1 to 3 and Figs. 13 to 15 represents a marked advance over the mirror oscillograph recording optical systems of the prior art. In the latter optical systems, the illuminated opening is imaged immediately at the slit, and hence the light flux from the opening diffused at thev oscillograph mirror, in both their! co-ordinate planes. For that reason, the'mirror aperture is the limiting aperture of those optical systems also in the co-ordinate plane which contains the mirror axis. Since the physical size of the oscillograph mirror must be comparatively small in order to avoid distortions due to its mass, the above condition has been a serious obstacle to an eilicient utilization of the light flux in the prior art optical systems. The advantage gained in Y this respect by the imagery recording to the present invention is considerable because, as is well known to those. skilled in the art, the emciency with which the light flux from a given lightsource is utilized in an optical system, is approximately proportional to the product of the limiting apertures in the two co-ordinate planes of the optical system.

In orderto elaborate on the above explanations and also to aflord a convenient comparison between the imagery performed in the prior art optical systems and the imagery performed in the optical systems Of Figs. 1 to 3 and Figs. 13 to 15,- two prior art mirror os'cillograph recording optical systems are illustrated in Fig. 16, and Figs. 17A and 173, respectively. Figs. 16, 17A, and 17B, are diagrammatic longitudinal sections in which the optical axis is represented as a straightline and the oscillograph mirror as an aperture.

In this respect, therefore, and also in all other pertinent respects, the diagrams of Figs. 16, 17A. and 17B, conform to those of Figs. 2, 3, 14, and 15. Moreover, parts employed in the prior art optical systems as well as in the optical systems of Figs. 1 to 3 and Figs. 13 to 15 are designated in Figs. 16, 17A, and. 178, by the same reference characters as in Figs. 2, 3, 14, and 15.

Referringnow to Fig. 16, this figure shows the imagery most commonly performed in the prior art optical systems. Fig. 16 is a section in the horizontal plane but, since only spherical lenses are employed in the optical system, it illustrates also the imaging actions in the vertical plane except insofar as the action of spherical lens 59- in the vertical plane is barred by screen 22 in the same manner as inthe optical system of Figs. 13 to 15. It will thus be seen that recording point 27 is, in the optical system oi Fig. 16, again conjugate to the horizontal slit 2| in ,thetween.

' ordinate planes because the sphericallens ll has power in both the vertical andhorlzontal planes.

Spherical lens ".too, has power in both the rem-- cal and horizontal planes. and its' action in-either co-ordinate planeis not superseded byza'nother imaging action as is thecase in; the optical .systems of Figs. 1 to 3 and Figs.-13to 15. Opening l3; therefore, now is imaged immediately at slit 2|- m the two poo-ordinate, planes. The light flux from opening 13 thus is diffusedat mirror-11in the two co-ordinateplanes so that the limiting aperture in both planes isthe apertureAof mirror 11., That is to say, the aperture of'spherical lens is, as seen from slit 2|, is'filled with light" flux from opening it only to the'e'xtent permitted by'the size of aperture A, and thiscondition cannot be remedied. by enlarging the aperture'of spherical lensll. But in the optical systemsof Figs- 1 to v3, and Figs. 13 to 15, the'aperture'of cylindricallenses 24 and 56, respectively,-can be made, as large as it is practical-to make it. For

any given size of their aperture, cylindrical lenses 24 and 58 will be completely filled with light flux from the opening in screen I by virtue of the i.

' fact that this light flux is iocussed substantially on mirror II by the action of cylindrical lenses l5 and 55, respectively, in the same co-ordinate plane in which cylindrical lenses 24 and 56 act.

The prior art optical system illustrated in Figs.

17A and 17B differs from that of Fig. 16 ,in-that the three spherical lenses l2, l9, and 86,-ofthe latter optical system are replaced in the former optical system by three pairs of cylindrical lenses m and 9"), 92a and 92b, and 93a and 93b, respectively. The two cylindrical lenses of-which each pair is made up, have their cylinder axes at a right angles to-one another and, furthermore,

have the same parts of the optical systeinat their conjugate foci, That is .0 S cylindrical lenses Bid and 91b have their cylinder axes at right angles to one another, and ,each lens has one of itsconjugate tool at lamp filament i0 and the other at mirror l1. Cylindrical lenses 92a and 92b, in their turn, have their cylinder axesat right angles to one another, and each lens has one of its conjugate foci-at opening 13 and the other at slit 2|. I Cylindrical lenses 93a and 93b, finally, have their cylinder axes at right angles jto one another, and each lens has one of its conjugate foci at slit 2 cording point 21.

As in theoptical system of, Fig.-16, therefore, 1 opening," is imaged inthe optical system of Figs. 17A andv 173 immediately at slit 2i in the two'co-ordinate planes. This result is accomplished because cylindrical lens 92a actsin the vertical plane (Fig. 17A) and cylindrical lens 925" in the horizontal plane (Fig. 173), and because both lenses have their conjugate foci at opening l3 and slit 2i, respectively, The light flux from opening l3 hence is diffused at mirror." in both co-ordinate' planes so that the aperture -A of mirror i1 is the limiting aperture also in the two co-ordinate planes'of theoptical system of Figs. 17A and 17B. Again, this conditiongcani not beremedied by enlarging the aperturesbi' cylindrical lenses 92a and 9212 since these apertures, as seenfrom slit 2|, are filled with-light flux from opening. I 3 only to the extentpermit-y ted by the size of aperture It should be noted that, on

sition between screen It and mirror II, cylindricallens Sib slightly affects the action of cyl and the other atjre account of its poplane, at the conjugate foci of a lens combination consisting of cylindrical lenses Slb and 92b.

- But this does not alter the fact that the light flux from opening I3 is difiused at mirror I! also in the horizontal plane. Since, taken by itself, cylindrical lens 9Ib has lamp filament I and mirror I! at its conjugate fool, the combined action of cylindrical lenses 9Ib and 921) does not result in the formation of an intermediate image of opening I3 substantially on mirror II. The formation of this intermediate image, however, is the only way of avoiding the diffusion of the light flux from opening I3 at mirror [1, and hznce a prerequisite to the removal of aperture A as the limiting aperture in one co-ordinate plane of the optical system.

Referring now again to the optical systems of Figs. 1 to 3 and Figs. 13 to 15, another advantage of having mirror I'I substantially at a common focus of two imaging means which act in only the co-ordinate planecontaining its axis, is that small deviations of mirror I! about an axis at right angles to its axis have a negligible efiect on the imagery in that plane. That is to say, mirror I'I need accurately be adjusted only about the horizontal axis I8I8 in the optical system of Figs. 1 to 3, and only about the vertical axis 5858 in the optical system of Figs. 13 to 15. This greatly increases the ease Of adjustment of the optical system, and is particularly important when it is necessary to replace the oscillograph galvanometer on which mirror I1 is mounted.

A further advantage of the novel imagery embodied, by way of example, in the optical systems of Figs. 1 to 3 and Figs. 13 to 15 results from the fact that there is formed substantially on mirror II an image of lamp filament III by the action of spherical lens I2 in the co-ordinate plane at right angles to the mirror axis, and simultaneously the intermediate image of the illuminated opening in screen II by the action of cylindrical lenses I and 55, respectively, in the co-ordinate plane containing the mirror axis. It thus is possible so to control the light fiux which enters the optical systems through the opening in screen I4 that it is all incident within the working aperture of mirror I I. This result is best obtained when the focal length of spherical lens I2 and the position of lamp II are chosen so that, in the first mentioned plane, the image of lamp filament I0 has a dimension no larger than that of mirror I I, and when the focal length of cylindrical lenses I5 and 55, respectively, and

the position of screen I4 are chosen so that, in the second mentioned plane, the largest dimenslon which the intermediate image may have, is no larger than the dimension of mirror II. If these conditions are fulfilled, all the light flux passing through the opening in screen I4 is subject to control by mirror I'I, whereby the formation of stray light in the optical systems is reduced to a negligible amount.

The optical systems shown in Figs. 1 to 3 and Figs. 13 to as embodying the imagery according to the present'invention may be modified'as follows without affecting the basic principles of their operation which have been set forth hereinabove.

(l) Condenser lens I2 is shown in Figs- 1 to 3 and Figs. 13 to 15, and has been described hereinabove, as being spherical. lit-hence acts in the two co-ordinate planes of the optical systems. However, as has been pointed out hereinabove,

14 its action in the co-ordinate plane which contains the axis of vibra'tion'of mirror I1, is immaterial as far as the novel imagery disclosed in this specification is concerned. ,Spherical condenser lens I2, therefore, may be replaced by a cylindrical condenser lens which has its cylinder axis parallel to the axis or mirror I! and hence acts in only the co-ordinate plane at right angles to the mirror axis.

For example, in the optical system of Figs. 1 to 3 wh.rein mirror axis I'8I 8 is horizontal, spherical lens I2 may be replaced by'a cylindrical lens 55 which has its cylinder axis horizontal and hence acts in only the vertical plane. Like spherical lens I2, cylindrical lens 65 has one of its conjugate feel at lamp filament Ill, and the other substantially at mirror II. may, furthermore, have the same position as spherical lens I2, in which position it is shown in Fig. 18. But since it acts in only the vertical plane, it may also have any other position between lamp II and mirror I! which is consistent with its function to image lamp filament I9 substantially on mirror I'I. Correspondingly, spherisal lens I2 may be r.placed in the optical system of Figs. 13 to 15 wherein mirror axis 58---58 is vertical, by a cylindrical lens which has its cylinder axis vertical and hence acts in only the horizontal plane.

In designing an actual optical system with a cylindrical condenser lens, however, the extension of lamp filament II) .in the direction parallel to the mirror axis should be made so great that the opening in screen I4, as seen from cylindrical lenses I5 or 55, is completely filled with light.

(2) It has been explained hereinabove that, while spherical lens ,I9 has power in the two coordinate planes of the optical systems, its action in the co-ordinate plane which contains the axis of vibration of mirror I1, can be disregarded.

Y Spherical lens I9 may therefore be replaced by a cylindrical lens which has its cylinder axis parallel to the axis of mirror I! and hence acts in only the coordinate plane at right angles to that axis. For example, in the optical system of Figs. 1 to 3 wh;rein mirror axis I8 -I 8 is horizontal, spherical lens I9 may be replaced by a cylindrical lens 66 which has its cylinder axis horizontal and hence acts in only the vertical plane. Correspondingly, spherical lens I9 may be replaced in the optical system of Figs. 13 to 15 wherein mirror axis 58-58 is vertical, by a cylindrical lens 51 which has its cylinder axis vertical and hence acts in only the horizontal plane. Lik spherical lens I9, cylindrical lenses 66 and 61 have one of their conjugate foci at the opening in screen I l, and the other at slit 2I.- Cylindrical lenses 65 and 61 may, furthermore, have the same position as spherical lens I9, in which position they are shown in Figs. 19 and 20, respectively. But since they act in only the co-ordinate plane at right angles to the axis of mirror I'I, they may have any other position between screens I4 and .22 which is consistent with their function to image the opening in screen I4 in the plane of silt 2|.

Spherical lens I9, on the other hand, should be placed close to mirror I1, as shown in Figs. 1 and 13, list it interfere with the imagery in the coordinate plane which contains the mirror axis.

(3) When the light beam defined by lamp filament I0 and the opening in screen It is incident upon mirror H at a sufflciently small angle, the two cylindrical lenses I5 and 24, and 55 and 55. respectively, may be replaced by a single cylin- Cylindrical lens 65 drical lenses l and 24 may be replaced by a single cylindrical'lens H as shown in Fig. 2|.

Like cylindrical lenses l5 and 24, cylindrical lens H has its cylinder axis vertical, and it is placed so as to be travers-d by the reflected as well as the incident part ofthe light beam proceeding through the optical system. The relative focal length of cylindrical lens H is so chosen that the openingin screen l4 and a position on, or close to. mirror II are conjugate with respect to cylindrical lens II on the incident part, and this position and slit II are conjugate with respect to cylindrical lens II on the reflected part of the light beam. In this manner, cylindrical lens H forms the intermediate image of the openingin screen H substantially on mirror I! and, simultaneously, images the intermediate image in the plane of slit 2!.

correspondingly, cylindrical lenses 55 and 56 may be replaced in the optical system-.of Figs.

13 to 15 wherein mirror axis 58-58 is vertical, by a single cylindrical lens which has its cylinder axis horizontal.

The angle at which the light beam is incident upon mirror H, may be made sufficiently small by'considerably lengthening the optical systems mechanically. However, this end may be accomplished in a. more convenient way which, at the same time, provides for a very compact mechanical design of the optical systems and which is shown in Fig. 21 as applied, by way of example,

to the optical system of Figs. 1 to 3. It consists of placing a. reflecting prism I0 between screen 14 and mirror I! whereby the light beam is folded so that it is incident upon mirror 11 at a small angle and cylindrical lens H is traversed by both the incident and reflected parts of the light beam. In place of prism there may be employed other suitable bram folding means such as mirrors, or the like.

For the reasons stated hereinabove, cylindrical lens II should preferably be well corrected when it is substituted for cylindrical lenses l5 and 24, and a variable area track is to be produced with the optical system of Figs. 1 to 3'.

(4) If it is desired to employ the optical systems of Figs. 1 to 3 and Figs. 13 to 15 for record- "ing sound in accordance with the method generally known as "noiseless recording, the well known ground noise reduction systems may be used in conjunction therewith, as will easily be understood by those skilled in the art.

Many other modifications of the invention will readily suggest themselves to those skilled in .the art. The invention, therefore, is not to be limited, except in so far as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed is:

wards said recording point; means forming said slit, said slit forming means being placed between said mirror and said recording point; and a cylindrical lens placed bztween said screen and said mirror, and having its cylinder axis at right angles to said axis; said cylindrical lens being traversed by said incident and reflected parts, said opening and said mirror being conjugate with respect to said cylindrical lens on '1. In an optical system of the class described,

and in which the, recording point is conjugate to a slit in the two co-ordinate planes, the combination of a mirror adapted to vibrate about an axis, said axis being contained in one of said co-ordinate planes; light beam defining means which include a light source and a screen with an opening; said opening being illuminated by said light source and said light beam being deflected by said mirror so as to have a part which is incident from said opening upon said mirror, and a part which is reflected from said mirror tosaid incident part, and said mirror and said slit being conjugate with respect to said cylindrical lens on said reflected part.

2. In an optical system of the class described. and in which the recording point is conjugate to a slit in the two co-ordinate planes, the combination of a mirror adapted to vibrate about an axis, said axis being contained in one of said co-ordinate planes; light beam defining means which include a light source and a screen with an opening, said opening being illuminated by said light source and said light beam being deflected by said mirror so as to have a part which is incident from said opening upon said mirror, and a part which is reflected from said mirror towards said recording point; means forming said -slit, said slit forming means being placed between said mirror and said recording point; means placed between said screen and said mirror for folding said incident part; and a cylindrical lens placed between said folding means and said mirror, and having its cylinder axis at right angles to said axis: said cylindrical lens being traversed by said incident and reflected parts, said opening and said mirror being conjugate with respect to said cylindrical lens on said incident part, and said mirror and said slit being conjugate with respect to said cylindrical lens on said reflected part.

3. In an optical system of the class described, and in which the recording point is conjugate to a horizontal slit in both the vertical and horizontal planes, the combination of a'. mirror adapted to vibrate about a horizontal axis; light beam defining means which include means for forming a light spot of vertically graded light flux,

said light beam being deflected by said mirror so as to have a part which is incident from said light spot upon said mirror, and a part which is reflected from said mirror towards said recording point; means placed between said light spot and said mirror for folding said incident part; means placed between said mirror and said recording point, and forming said slit; a cylindrical lens placed between'said folding means and said mirror and between said mirror and said slit forming means, said cylindrical lens having its cylinder axis vertical and being traversed by said incident and reflected parts; and imaging means placed in front of said mirror andacting in the vertical plane: said light spot and said mirror being conjugate with respect to said cylindrical lens on said incident part, said mirror and said slit being conjugate with respect to said cylindrical lens on said reflected part, and said light spot and said slit being conjugate with respect to said imaging means.

4. In an optical system of the class described, and in which the'recording point is conjugate to a horizontal islit in both the vertical and horizontal planes, the combination of means for forming a light" spot of vertically graded light flux; a mirror adapted to vibrate about a horizonimaging means placed in front of said mirror;

and having fifth and sixth conjugate foci: said first imaging means acting in only the horizontal plane and having said first focus at said light spot, and said second focus substantially at said mirror so that an intermediate image of said light spot is formed substantially on said mirror; said second imaging means acting in only the horizontal plane and having said third focus at said intermediate image, and said fourth focus at said slit; and said third imaging means acting in the vertical plane and having said fifth focus at said light spot, and said sixth focus at said slit.

5. The combination defined in claim 4 wherein said first imaging means is a cylindrical lens having its cylinder axis vertical. 2

6. The combination defined in claim 4 wherein said first and second imaging means are each a cylindrical lens having its cylinder axis vertical.

7. The combination defined in claim 4 wherein said third imaging means is a spherical lens.

8. The combination defined in claim 4 wherein said first and second imaging means are each a cylindrical lens having its cylinder axis vertical, and said third imaging means is a spherical lens.

9. In an optical system, the combination of a light source; a screen with an opening whose horizontal extension varies in a vertical direction,

said opening being uniformly illuminated by said 8 fourth conjugate foci; a second cylindrical lens placed between said mirror and said slit forming means, and having fifth and sixth conjugate tool; a second spherical lens placed in front of said mirror, and having seventh and eighth conjugate foci; and a microscope objective placed between said slit forming means and said recording point, and having ninth and tenth conjugate foci: said first spherical lens having said first focus at said light source, and said second focus substantially at said mirror; said first cylindrical lens having its cylinder axis vertical and having said third focus at said opening, and said fourth focus substantially at said mirror so that an intermediate image of said opening is formed substantially on said mirror; said second cylindrical lens having its cylinder axis vertical and having said fifth focus at said intermediate image, and said sixth focus at said slit: said second spherical lens having said seventh focus at said opening, and said eighth focus at said slit; and said microscope objective havingsaid ninth focus at said slit, and said tenth focus at said recording point.

JOHN A. MAURER, 5:.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,847,638 Taylor Mar. 1, 1932 1,999,721 Dimmick Apr. 30, 1935 2,036,622 Emmerich Apr. 7, 1936 2,052,220 Dimmick Aug. 25, 1936 2,121,568 Newcomer June21, 1938 2,125,890 Cook Aug. 9, 1938 2,157,166 Dimmick May 9, 1939 2,173,681 Dimmick Sept. 19, 1939 2,256,402 McLeod Sept. 16, 1941 

